1. Field of the Invention
The present invention relates to a deposition method and apparatus having a uniform deposition rate and good reproducibility.
2. Discussion of the Background
Electroluminescence display devices are expected to be the next generation of emissive display devices due to their wide viewing angles, high contrast, and high response speed.
Electroluminescence display devices may be classified as either organic light emitting display devices or inorganic light emitting display devices according to the material used to form an emission layer (EML) included therein. Organic light emitting display devices are brighter and have higher driving voltages and higher response speeds than inorganic light emitting display devices. Organic light emitting display devices can also display color images.
An organic light emitting diode (OLED) includes an inner layer located between two electrodes. The inner layer may include a variety of layers including a Hole Injection Layer (HIL), a Hole Transport Layer (HTL), an EML, an Electron Transport Layer (ETL), an Electron Injection Layer (EIL), or the like. These layers are known as organic thin films.
Organic thin films such as the HIL, HTL, EML, ETL, EIL or the like can be formed on a substrate using a deposition method in a deposition apparatus.
During a deposition method, a thin film is fabricated on a substrate in a vacuum chamber by heating a heating crucible to evaporate or sublimate an organic material to be deposited.
The organic material forming the thin film of the OLED is evaporated or sublimated at a temperature range of 250° C. to 450° C. and at a degree of vacuum of 10−6 to 10−7 torr. The material used to form the electrodes usually evaporates at a higher temperature than the temperature at which the organic material evaporates, but the evaporation temperature of the electrodes varies according to the type of electrode material used. Electrode materials, such as magnesium (Mg), silver (Ag), aluminum (Al), and lithium (Li) evaporate at temperatures of about 500° C. to 600° C., 1000° C., 1000° C., and 300° C., respectively.
It is vital that the film deposited on the substrate has a uniform thickness. A variety of methods can be found in the prior art that attempt to optimize the uniform thickness of the film deposited on the substrate. In one conventional method, the substrate may be rotated and the distance between a single deposition source and the substrate may be maximized to optimize the uniform thickness of the film. But it is impossible to increase the distance between the single deposition source and the substrate to the distance needed to deposit a film of uniform thickness due to equipment constraints. Therefore, a single deposition source cannot produce a film of uniform thickness on a substrate due to the incidence angle of the deposition material when the substrate is rotated.
A symmetrical multi-deposition source has been used in the prior art to minimize the distance between the deposition source and the substrate in an attempt to optimize the uniform thickness of the film. But the thin film deposited on the substrate did not have a uniform thickness due to the positions of the deposition sources. Many deposition sources are required to solve this problem, which becomes prohibitively expensive.
It is more difficult to achieve a uniform thickness of the thin film when the symmetrical multi-deposition source uses a mask to deposit the thin film on the substrate because a shadow effect is produced between the mask slits and the substrate. The distance between the substrate and the deposition source must be maximized to overcome the shadow effect.
The distance between the substrate and the deposition source is a vital factor in maintaining the uniform thickness of the film. The film thickness will be more uniform if the distance between the substrate and the deposition source is increased. But a larger distance between the substrate and the deposition source reduces the deposition rate, changes the characteristics of the material to be deposited, and requires more equipment.